How did phone dial tones get recognized on the telephone office end?

Question

OK, from what I understand, dial tones replaces manual telephone office operators. Instead of having them connect you to your number, the numbers you press correspond to particular frequency which get recognized automatically by a computer and automatically connects you to that number

Except, how do the tones even get recognized? I use audacity for instance which has a pitch recognition feature. It’s… Not the best and can and will get things wrong on crystal clear audio

Phone audio on the other hand? The connection would be weak, someone playing or shouting something in the background could mess with the dial tone data sent to the office (of which I am aware phreaking exploited)

It’s the late 70’s. How did the telephone office computers recognize the tones perfectly and without error? All it takes is someone shouting or playing something in the background or a telephone microphone with terrible frequency response, or electromagnetic interference to mess with the dial tone data sent to the office and confuse it

This could cause everything from numbers never going through, to connecting one to the wrong number, yet this never happened, on 70’s tech no less

What did they do for crystal clear tone recognition in the 70s that my audio software on my 2019 laptop can’t?

In: Technology

Answer 1

To add to what others have said, there is the older technology of pulse dialling that was developed in the 1890s the was standard until tone dialling was developed in the 1960s. In a pulse dial phone you would put your finger in the hole on the dial corresponding to the digit to dial, rotate it to the stop position and release it. As the dial rotated back to its rest position, it generated a series of electrical pulses. The higher the number the further dial rotates, so the more pulses get generated. At the exchange, a machine counts the pulses and rotates an electrical switching device by the number of pulses, stopping once the pulses end, making the connection for that digit. While tone dialling was invented in the 1960s, it took time for exchanges to be updated, and more modern exchanges could cope with both pulse and tone dialling.